1. Field of the Invention
The invention relates to compensating devices, and more particularly, to a receiver with baseline wander compensation applicable to a network system, such as Ethernet to prevent baseline wander interference.
2. Description of the Related Art
When data is transmitted between main systems of two ends via Ethernet, a transmission system is served as a transmission medium. As illustrated in FIG. 1, the transmission system includes a transmitter 10, a sending coupler 12, a transmission channel 14, a receiving coupler 13 and a receiver 11, such that a receiver main system 21 receives signal from a transmitter main system 20 via the transmission system.
The transmission channel 14 of the transmission system includes a transmission interface such as a twisted-pair wire, an optical fiber or a coaxial cable. Since the sending coupler 12 and the receiving coupler 13 are electrically insulated devices, damages to transmission system caused by receiving specific signals are prevented. However, due to the electrical properties of the sending coupler 12 and the receiving coupler 13, a magnetic coupling effect is produced to prevent a passage of direct current (DC) therethrough. As a result, the input signal sent to the receiver 11 has a exponential index degraded. That is, a baseline wander effect is produced to increase the bit error at the receiver end of the transmission system. Thus, it is a major issue of a network transmission industry to eliminate occurrence of the baseline wander in the transmission system.
In the U.S. Pat. No. 6,415,003, a conventional baseline wander correction circuit is proposed as illustrated in FIG. 2. The conventional baseline wander correction circuit is formed in the receiver 11′, wherein the baseline wander correction circuit adds an ADC reference voltage generator 112 between an ADC 110 and a slicer 111 of the receiver 11′, such that the ADC 110 receives a reference voltage Vref from the ADC reference voltage generator 112. At an initial stage of the transmission, the reference voltage Vref is determined based on the cable length to prevent clipping of the communication signal input to the ADC, and with cooperation of a digital baseline wander correction circuit, the baseline wander effect is eliminated.
However, such baseline wander correction circuit still contains several drawbacks. The ADC reference voltage generator 112 needs to generate different reference voltages Vref according to the length of the transmission channel 14′ (such as twisted-pair wire) or parameters related to the length of the transmission channel 14′. In order to match the reference voltage Vref provided by the ADC reference voltage generator 112 with the common length (e.g. 1-120 m) of the transmission channel 14′, the reference voltage Vref is normally set to be 2 volts over a short cable length, whereas the reference voltage Vref is set to be 1.33 volts over a long cable length. Although larger reference voltage Vref can effectively prevent receiving data error of the receiver 11′ caused by baseline wander interference, the resolution of the ADC 110 is on the other hand degraded.
Therefore, it is a current issue for the transmission system to prevent baseline wander interference without affecting the resolution of the ADC at the same time.